Heat erosion resistant alloy



Patented May 28, 1940 PATENT OFFICE HEAT EROSION RESISTANT ALLOY George Charlton, Detroit, Mich., assignor Eaton Manufacturing Company,

Cleveland,

Ohio, a corporation of Ohio No Drawing. Application May 6, 1939, Serial No. 272,131

\ 2 Claims.

This invention relates to a steel alloy'and more particularly is concerned with a readily machinable, erosion and corrosion resistant, steel alloy that retains its: physical properties at elevated 5 operating temperatures of several hundred degrees Fahrenheit when fabricated into metal engine parts especially as used in valves and the like for internal combustion engines.

The primary object of this invention is the provision of an alloy steel of new composition which will be readily machinable or forgeable and still be resistant to hot erosion ranging from a low red heat to temperatures as high as 1800 F., and yet possess good cold wear-resistance; from which alloy as above described, engine parts, especially valves and the like of the hollow cavity type, may be fabricated.

A further object of this invention is the provision of an alloy steel which when fabricated into an engine part will provide a retention of hardness of surface under normally elevated operating temperatures, and in addition a hot strength at these elevated temperatures for extended periods of time.

Present alloy materials which afiord ease of fabrication are generally deficient in other desirable properties necessary, for example, to produce an acceptable exhaust valve, due to lack of resistance to the hot erosive effect of gases during operation in an engine, also lack of hot hardness, this particular property being required to withstand the impact hammering of the valve seat of the valve when it is operating at several hundred degrees Fahrenheit, and. the retention of hardness for prolonged periods of time at these elevated operating temperatures.

Certain combinations of elements have provided one or more of the above desirable properties enumerated in conjunction with the several 40 properties necessary to produce acceptable poppet valves, but no combination of elements, insofar as this applicant is able to determine, has resulted in a commercially workable alloy. This is to say, an alloy which can be fabricated by forging and machining by commercial methods and which, when fabricated, will result in a composition of -a high order of the several properties above referred to from which may be suitably engines, possesses a high degreeof hot hardness and wear-resistance under elevated working temperatures, but such materials are unforgeable and unmachinable commercially.

It is also known that relatively high percentages of a combination of the elements manganese-chromium possess merit .as a hot erosion resistor to engine exhaust gases, and in addition hot and cold wear-resistance, but such a combination of elements in an alloy renders it difilcult to forge and is unmachinable from a commercial aspect as concerns certain types of poppet valves.

It is also known that a combination of elements of relatively high chromium-nickel content can be readily fabricated into poppet valves because of the ability to forge and machine them commercially. An alloy part of this type, however, is deficient in its ability to resist hot erosion,

lacks retention of hardness when subjected to elevated operating temperatures, and is short on cold wear-resistance. Other chromium-nickel materials in which the nickel constituent is very high possess good hot erosion properties, but again the inherent softness of these materials makes it necessary to add other materials and processes to certain parts of the surface to supply necessary properties which the materials lack. Therefore, an engine part formed from this type of alloy, in order to be commercially successful, must be supplemented by the addition of other materials and processes which supply the surface texture. of the part with the deficient properties.

The three known combinations of controlling elements mentioned above and present in relatively high percentage, are:

1. Chromium, cobalt, tungsten 2. Chromium, manganese 3. Chromium, nickel.

4. Chromium, manganese, cobalt. The fourth combination provides an entirely new series. It is apparent from the first three alloy series mentioned that the elements, chromium, cobalt, nickel, and manganese, when used in percentages which make them controlling factors, are elements which contribute to the building up of properties desirable in materials used for poppet valves. By making a new series'in which the elements, chromium, manganese, and cobalt predominate a greater number of desirable properties are produced than is contained in the first, second, and third series. With these elements considered as the controlling elements, they can be further assisted by small percentages of tungsten, molybdenum, silicon, aluminum, zircon, boron, and carbon.

An alloy steel containing as its essential elements cobalt-chromium and manganese within the range of the present invention and provided in addition with suitable amounts of a group of other elements, as hereinafter stated, has resulted in the provision of the alloy of this invention embodying a composition of the properties of forgeability, machinability, hot erosion resistance, hot hardness, retention of hardness for sustained periods of time and other secondary properties.

The special purpose for which this alloy was originally designed was for hollow head and stem poppet valves as used in high speed internal combustion engines, wherein they are subjected to normally elevated operating temperatures and highly oxidizing conditions especially when the engine is operated on a fuel containing tetraethyl lead. However, the alloy is equally as well adapted to use in a part of a similar nature or when subjected to similar operating conditions, and while its use and application to an internal combustion engine valve is described, it is to be understood it also includes the application of this alloy into any casting, or use, subjected to similar operating conditions.

An alloy steel composed in part of the controlling elements as hereinbefore stated and in accordance with this invention has an analysis substantially as follows:

Percentage Carbon 1.00 Manganese 1 5.00 Chromium 25.75 Silicon .70 Tungsten 1.25 Cobalt 16 .25 Nickel 3.30 Molybdenum 1.32 Iron Balance characteristics of the alloy of this invention.

The elements phosphorus and sulphur are present in quantities common to most all steel alloys, however, in order that these elements will not have an adverse effect upon the good forging properties of this alloy they are preferably maintained as low as possible in the total percentage. The presence of aluminum, vanadium, zirconium and boron may be introduced into the alloy through the use of scrap stock in preparation of the alloy metal or through the use of ferrous alloy additions-which are added to the charge to obtain the proper percentages of the principal alloying elements. Their presence, however, in small percentages does not affect the characteristic properties of the controlling elements and in reality may be advantageous for their refining and cleansing influence.

While the foregoing analysis sets forth a particular percentage of elements in producing one heat of the alloy it is obvious that a range in variation of these percentages between certain limits may be made, producing slightly different grades of the alloy, without departing from the broad properties disclosed for the alloy of this invention. Very good results have been obtained by the use of the following workable range of the elements between the limiting percentages:

Percentage Carbon .25 to 1.50 Manganese 5.00 to 20.00 Chromium 15.00 to 30.00 Silicon; .25 to 1.50 Cobalt 5.00 to 30.00 Nickel .50 to 3.50 Tungsten .50 to 2.50 Molybdenum .50 to 2.50 Iron -1 Balance This alloy has been found to have among others the following properties:

It is an excellent corrosion resistor. Tested for resistance to the erosive effect of tetra-ethyl gases at high temperatures itexhibited values comparable to Stellite, which has generally been used as a criteria, but is a material that cannot be forged and machined to produce an entire valve while on the other hand this alloy has been forged and machined.

The hardness value of the particular alloy first mentioned is approximately 44 Rockwell, measured on the C-scale, this being high for a material which can be machined and fabricated; and this hardness is retained when the stock is subjected to long periods at high temperatures, as evidenced by a sample heated for fifty'hours at 1000 F. the hardness increased slightly, and when retained for two hundred hours at temperatures ranging from 600 F. to 1800 F. the hardness was approximately 42 Rockwell, measused on the C-scale. This clearly demonstrates retention of hardness under elevated operating temperatures which in turn evidences sustained resistance to wear.

It is an excellent oxidation resistor. A sample exposed for eight hours to a temperature of 1750" F. remained bright in appearance and free from oxidation.

From a study of the above properties of this alloy it will be readily apparent that the alloy is to be sharply distinguished from other ferrous alloys devised for the purposes stated and other similar uses or conditions, especially from extremely hard and substantially unmachinable alloys as is usual with wear resistant alloys of this character, and formal changes may be made in the elements from the limited percentages disclosed without departing from the workable range of elements as previously stated and to which the characteristic properties of this alloy is believed confined as covered in the appended claims.

What I claim is:

1. A non-oxidizing. heat erosion and corrosion resistant alloy comprising carbon .25% to 1.50%, manganese 5.00% to 20.00%, chromium 15.00% to 30.00%, silicon to 1.50%, cobalt 5.00% to 30.00%, nickel 50% to 3.50%, tungsten v50% to 2.50%, molybdenum 50% to 2.50%, and the balance iron, said alloy characterized by ready machinability and forgeability.

2. A non-oxidizing, heat erosion and corrosion resistant alloy comprising carbon 1.00%, manganese 15.00%, chromium,25.75%, silicon .'70%, tungsten 1.25%, cobalt 16.25%, nickel 3.30%, molybdenum 1.32% and the balance iron.

GEORGE CHARLTON. 

